1. Field of the Invention
The present invention relates to chemical sensors for remote monitoring, using nanostructures as low-power sensor elements.
2. Description of Related Art
Advances in integrated circuit technology have enabled complex computers to be made small, lightweight, and relatively inexpensively, often as integrated microprocessors. In addition, they can be made to consume relatively small amounts of power. Computers in this class are not as sophisticated as state-of-the-art personal computers, but are powerful enough to process 16-bit data and do floating-point arithmetic. Because they require so little power, they can be used in devices that run on batteries for relatively long periods of time. Thus, for example, they are useful for applications as diverse as burglar alarms and cell phones.
At the same time, modern communications technology enables computers to exchange information wirelessly. Various protocols for radio communication allow data transmitters to use radio spectrum for brief periods of time in limited regions of space. Using such protocols, computers can communicate using weak radio transmitters that transmit and receive in short pulses. This approach minimizes the power requirements of radio communication. As a result, battery-powered devices can transmit data wirelessly to base stations, while remaining in operation for a relatively long period of time without changing or recharging their batteries. Such devices can be used together as a network of remotely located computers.
One important application for a sensor remote network is monitoring of conditions over a wide area. The use of batteries and radio communication eliminates the need to install wires to connect widely deployed monitors. For example, remote battery-powered sensors are known for monitoring electromagnetic radiation along the length  of electric power lines, or the monitoring of water quality over a wide area, using distributed optical sensors. However, it is generally believed that a power source is needed to recharge the batteries to maintain such remote sensors operational for sufficiently long periods.
One type of sensor is a chemical sensor, which measures the presence or absence of a chemical species. A variety of chemical sensors are known in the art; for example optical sensors and catalytic bead sensors. Sensors of this type are often relatively inexpensive, sensitive and specific to particular chemicals. However, they are large, and often operate at high temperature, and require large amounts of power. Another type of chemical sensor is a surface acoustic wave detector. These sensors are often smaller and lighter, but they often respond to a range of chemicals rather than to a specific chemical. Yet another type of chemical sensor is a field-asymmetric ion mobility spectrometer. These sensors are often small, but require large amounts of power, and they are relatively expensive. They are often reasonably specific sensors, but often they are not very sensitive. This list is not exhaustive of the known chemical sensors. It is meant to illustrate that the types of sensors differ widely with respect to their size, sensitivity, resolution, specificity, power requirements, cost, and other properties. Most sensors are not appropriate for use in low-cost, battery-powered, remotely communicating devices.
It is desirable, therefore, to provide a remote sensing device with wireless communication capability, that is both compact and inexpensive. It is further desirable to provide a device that can operate for extended periods on a limited power resource.